Combined tire pressure monitoring and keyless entry receiver

The present invention claims priority to U.S. Provisional Patent Application Ser. Nos. 60/276,210 filed Mar. 15, 2001; 60/269,959 filed Feb. 20, 2001; 60/276,325 filed Mar. 16, 2001; 60/298,258 Jun. 14, 2001; 60/290,923 filed May 15, 2001 and 60/352,489, filed on Jan. 23, 2002.

BACKGROUND OF THE INVENTION

This invention relates to a system for monitoring conditions within a tire, and specifically to a receiver assembly for receiving transmissions of varying modulations from sensor assemblies within each of the tires and from a remote keyless entry system. It is becoming increasingly desirable to continually monitor tire pressures in a motor vehicle during operation. Such constant monitoring of tire pressures allows an operator to maintain vehicle tire pressures within an optimal range to optimize fuel economy and handling performance.

Conventional methods of monitoring tire pressure include positioning a sensor within each wheel to monitor pressure. The sensor assembly typically emits a radio frequency (RF) transmission indicative of tire conditions. A receiver disposed within the vehicle receives the RF signal and actuates a messages or warning light to signal the operator of tire conditions.

Many motor vehicles include a remote keyless entry system including a key fob carried by an operator to actuate door locks or other features. The remote keyless entry system includes a receiver disposed within the motor vehicle to receive transmissions from the key fob and actuate vehicle systems in response to transmissions received from the key fob. It is known in some system to utilize the same type of transmission for the tire monitoring system as is used in remote keyless entry system.

Typically, a transmission is modulated either as an amplitude shift keyed ASK, or a frequency shift keyed FSK radio frequency. The ASK transmission modulation is best suited for applications in which the receiver and transmitter are relative stationary to each other. In addition ASK transmissions are favorable when there exists a relatively long distance between the transmitter and the receiver. However, an ASK transmission becomes disrupted when the receiver or transmitter is moving relative to one another. The FSK signal is suited for transmitters that are moving relative to the receiver because the amplitude remains essentially constant for the duration of any transmission. However, the FSK transmission has lower peak field strength than a comparable ASK transmission. The FSK transmission is specifically suited for use with the sensor assembly disposed within the tire and the ASK is suited for use with the remote keyless entry system.

Accordingly, it is desirable to develop a receiver capable of receiving both ASK and FSK transmissions to optimize the capabilities of both the tire monitoring system and the remote keyless entry system.

SUMMARY OF THE INVENTION

An embodiment of this invention is a receiver assembly comprised of an amplitude key shifted (ASK) receiver and a frequency shift keyed (FSK) receiver for receiving transmissions from sensor assemblies mounted within each of the tires, and from a remote keyless entry system.

A system for monitoring conditions within tires mounted to a motor vehicle includes five tires, each with a sensor assembly. Each of the sensor assemblies gathers data indicative of conditions within the tire and transmits that data to a receiver assembly. The receiver assembly in turn forwards that data to a vehicle controller. The vehicle controller will then process the data for display to the operator of the motor vehicle.

Each tire mounts to a rim and each sensor assembly is mounted within the rim and includes a valve stem and a circuit housing. The sensor assembly includes a sensor circuit disposed within the circuit housing. The sensor circuit includes a temperature sensor, a motion sensor and a pressure sensor. An RF transmitter receives data gathered by the sensors, and relays that data to the receiver.

Each transmission from the various sensor assemblies includes a unique identity code relating to a specific sensor assembly. An initialization or learning mode defines specific sensor assemblies disposed on a specific motor vehicle. Learning the specific identity codes of the sensor assemblies eliminates errant reception of other transmissions from other sensor assemblies installed on other motor vehicles within close proximity.

The data transmitted from each of the sensor assemblies to the receiver is transmitted at predetermined intervals. There is a probability that the receiver will receive two or more data transmissions from different sensor assemblies at the same time. The receipt of two or more data transmission simultaneously or overlapped is known as a data collision. The receiver will not recognize collided data or overlapping data transmission, therefore the current invention prevents overlapping data transmissions by varying the interval between data transmission in a random manner. Another factor considered in preventing signal collision is the transmission rate that affects the length of time required to transmit data indicative of tire conditions. The faster data is transmitted and received the lower the probability of data collision. The shorter the total transmission time, the lower the probability of signal collision.

The receiver assembly comprises an amplitude shift key (ASK) receiver and a frequency shift keyed (FSK) receiver. The FSK receiver receives signals from the sensor assemblies. The ASK receiver receives signals from a key fob for a remote keyless entry system to initiate the locking or unlocking of doors.

The ASK transmissions are favorable for situations where the transmitter and receiver are substantially stationary. The ASK radio frequency transmission is easily disrupted by abrupt changes in received field strength and therefore are not favorable for sending transmissions from a moving object such as the tires of a motor vehicle. However, the ASK provides for greater signal power which is desirable for the remote keyless entry system. The FSK transmissions are favorable for conditions were the transmitter or receiver are moving during data transmission. However, an FSK transmission is amplified upon receipt, effectively removing any amplitude disturbances.

The receiver assembly switches between the ASK receiver and the FSK receiver in response to a triggering event. The triggering event is the vehicle speed. At speeds indicative of traveling along a roadway, the FSK receiver is engaged. As appreciated, a motor vehicle traveling at speed along the roadway does not require reception of ASK transmissions from a remote keyless entry transmitter to unlock the doors of the motor vehicle. Conversely, a vehicle at rest or parked is unlikely to spontaneously encounter a tire puncture, and therefore at lower speeds the ASK receiver is engaged.

An intermediate condition is encountered when the motor vehicle is idling. In this condition, the receiver assembly engages the ASK receiver due to the low speed of the vehicle, however, the tire may become punctured or encounter a condition that changes conditions within the tire. The signal from the sensor assemblies includes an ASK wake up signal that proceeds the FSK signal transmitting data indicative of current conditions within the tire. The ASK wake up signal triggers the change over from the ASK receiver to the FSK receiver. The FSK receiver remains engaged until the FSK transmission is completed and the ASK receiver is reengaged.

The system of this invention includes a receiver capable of receiving both ASK and FSK transmissions to optimize the capabilities of both the tire monitoring system and the remote keyless entry system.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view of a motor vehicle including a tire monitoring and remote keyless entry system;

<figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional view of a tire including a sensor assembly;

<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view of the sensor assembly mounted within the tire;

<figref idref="DRAWINGS">FIG. 4</figref> is a side view of a sensor assembly;

<figref idref="DRAWINGS">FIG. 5</figref> is a top view of the sensor assembly;

<figref idref="DRAWINGS">FIG. 6</figref> is an exploded view of the sensor assembly;

<figref idref="DRAWINGS">FIG. 7</figref> is a schematic view of the circuit assembly within the sensor assembly;

<figref idref="DRAWINGS">FIG. 8</figref> is a schematic view of the components of a transmission from the sensor assembly;

<figref idref="DRAWINGS">FIG. 9</figref> is a graphical representation of the format of data packets comprising the transmission from the sensor assembly;

<figref idref="DRAWINGS">FIG. 10</figref> is a graph illustrating the effect of transmission rate on signal overlap in prior art systems;

<figref idref="DRAWINGS">FIG. 11</figref> is a graph illustrating how increased transmission rate prevents data overlap;

<figref idref="DRAWINGS">FIG. 12</figref> is a schematic view of the receiver assembly;

<figref idref="DRAWINGS">FIG. 13</figref> is a schematic view of a motor vehicle and an external triggering device to initialize the sensor assemblies;

<figref idref="DRAWINGS">FIG. 14</figref> is a schematic view of a method of determining sensor assembly position; and

<figref idref="DRAWINGS">FIG. 15</figref> is a schematic view of another embodiment of determining sensor assembly position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of this invention is a system for monitoring conditions within tires mounted to a motor vehicle <b>10</b> shown schematically in FIG. <b>1</b>. The motor vehicle <b>10</b> includes four tires <b>12</b> along with an additional tire <b>12</b> carried as a spare. Each of the tires <b>12</b> includes a sensor assembly <b>14</b>. Each of the sensor assemblies <b>14</b> gathers data indicative of conditions within the tire <b>12</b> and transmits that data to a receiver assembly <b>16</b>.

The receiver assembly <b>16</b> in turn forwards that data to a vehicle controller <b>18</b>. The vehicle controller <b>18</b> will then process the data for display to the operator of the motor vehicle <b>10</b> or to the remote keyless entry system <b>19</b> to actuate unlocking of doors <b>20</b> or other such functions as are known to a worker skilled in the art. Preferably the remote keyless entry system <b>19</b> is an active system requiring actuation, such as by depressing buttons on the key fob <b>22</b>, however, it is within the contemplation of this invention for passive remote keyless entry system that do not require a positive action by the operator.

Referring to <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, each tire <b>12</b> mounts to a rim <b>24</b>. Each sensor assembly <b>14</b> is mounted within the rim <b>24</b> and includes a valve stem <b>26</b> and a circuit housing <b>28</b>. The circuit housing <b>28</b> is preferably mounted within the tire <b>12</b> and the valve stem <b>26</b> extends from the circuit housing <b>28</b> outward to provide a means of filling the tire <b>12</b> with air. A sensor circuit <b>46</b> disposed within the circuit housing <b>28</b> preferably includes a pressure sensor <b>36</b>, a temperature sensor <b>32</b> and an accelerometer <b>34</b>.

Referring to <figref idref="DRAWINGS">FIGS. 4-6</figref>, the valve stem <b>26</b> is pivotally mounted to the circuit housing <b>28</b> to provide for use in rims <b>24</b> of various configurations. The valve stem <b>26</b> is pivotally mounted to the circuit housing <b>28</b> and locked in a desired pivotal location by a lock nut <b>30</b>. Pivotal adjustment of the valve stem <b>26</b> relative to the circuit housing <b>28</b> allows for use of the sensor assembly <b>14</b> with various configurations of wheel rims <b>24</b> (FIGS. <b>3</b> and <b>4</b>).

<figref idref="DRAWINGS">FIG. 7</figref>, is a schematic view of the sensor circuit <b>46</b> disposed within the circuit housing <b>28</b>. The sensor circuit <b>46</b> includes the temperature sensor <b>32</b>, the accelerometer <b>34</b> and the pressure sensor <b>36</b>. Each of the sensors <b>32</b>, <b>34</b> and <b>36</b> are of any configuration known to a worker skilled in the art. An RF transmitter <b>40</b> receives data gathered by the sensors <b>32</b>, <b>34</b>, and <b>36</b> and transmits that data to the receiver <b>16</b>.

A battery <b>38</b> powers the sensor circuit <b>46</b>. A battery monitor measure battery power and provides a warning indicator that is sent to the receiver assembly <b>16</b> when remaining battery power attains a desired level. The receiver assembly <b>16</b> forwards the low battery signal to the vehicle controller <b>18</b> and in turn to the operator. Preferably the life of the battery <b>38</b> is of an extended length such that any necessary battery change is infrequent throughout the life span of the motor vehicle <b>10</b>. A controller <b>44</b> controls how the RF transmitter <b>40</b> emits data indicative of tire conditions.

The sensor circuit <b>46</b> also includes a low frequency receiver <b>42</b>. The low frequency receiver <b>42</b> receives signals generated to initiate the transmission of an identity code <b>68</b> (<figref idref="DRAWINGS">FIG. 8</figref>) from the sensor assembly <b>14</b> in order to initialize and localize the sensor assembly <b>14</b>. Initialization of the sensor assembly <b>14</b> teaches the receiver assembly <b>16</b> the identity codes of each sensor assembly <b>14</b> installed on the motor vehicle <b>10</b> so that the receiver assembly <b>16</b> can ignore transmission received from sensor assemblies <b>14</b> of other motor vehicles. Localization teaches the receiver <b>16</b> and controller <b>18</b> the specific tire position of the sensor assembly <b>14</b> on the particular vehicle. The tire position includes left front tire, right front tire, left rear tire, and right rear tire.

Referring to <figref idref="DRAWINGS">FIG. 8</figref>, a transmission <b>64</b> emitted by the sensor assembly <b>14</b> includes an ASK wakeup signal <b>66</b>, an identity code <b>68</b> and a data signal <b>70</b>. The transmission <b>64</b> is a FSK transmission, except for the ASK wake up signal <b>66</b>.

Referring to <figref idref="DRAWINGS">FIG. 9</figref>, each data transmission <b>64</b> includes a number of data frames <b>72</b>. Preferably, three (3) data frames <b>72</b> are sent for each transmission <b>64</b>. The data transmitted from the sensor assemblies <b>14</b> to the receiver assembly <b>16</b> are transmitted at predetermined intervals <b>80</b>. There is a probability that transmissions from the various sensor assemblies <b>14</b> to the receiver assembly <b>16</b> will arrive at the same time (schematically indicated at <b>78</b>). The receipt of two or more data frames <b>72</b> simultaneously or overlapped, as shown at <b>78</b>, is known as a data collision. The receiver assembly <b>16</b> will not recognize collided or overlapping data transmission because the overlapped data frames <b>78</b> are of a greater duration than the receiver assembly <b>16</b> is programmed to receive. Overlapping data frames <b>72</b> cause the receiver assembly <b>16</b> to ignore the data frames <b>78</b>. Repeated data collisions would eliminate data transmitted from at least two of the sensor assemblies <b>14</b>.

The system of this invention includes a method of preventing repeated data collisions. The sensor assemblies <b>14</b> of this invention prevent overlapping data frames <b>72</b> by varying the predetermined interval <b>80</b> between data frames <b>72</b> in a random manner. The length of the data frame <b>72</b> is preferably 50 milli-seconds (ms) with the interval <b>80</b> varying according to the below listed equation. &lt;br /&gt;Interval length=standard length*(beta*standard length)

Where: interval length is the length of time in ms between data frames; <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0044">Standard length is a predetermined duration of time in ms; and</li><li id="ul0002-0002" num="0045">Beta is a random variable with a value between 0 and 1.</li></ul></li></ul>

Preferably the standard length of time is 100 ms; therefore the interval length will vary between 100 ms and 200 ms depending on the value of beta. Each transmission from the sensor assemblies <b>14</b> are sent with differing variable intervals <b>80</b>, such that even if one or more data packets <b>72</b> overlap for any one transmission, subsequent data packets <b>72</b> will not overlap, thereby preventing cyclical, or repeated overlap. As appreciated, differing intervals and lengths of data frames are within the contemplation of this invention, and a worker skilled in the art would recognize the application of this method to other lengths of data transmission.

In another embodiment of this invention, the length of the variable interval <b>80</b> is transmitted to the receiver assembly <b>16</b>. The receiver assembly <b>16</b> will then expect the next data packet <b>72</b> at the communicated interval. This allows the receiver assembly <b>16</b> to switch back to the ASK receiver between data frames <b>72</b>.

Another factor considered in preventing signal collision is the transmission rate. The faster data is transmitted and received the lower the probability of data collision. Prior art <figref idref="DRAWINGS">FIG. 10</figref> illustrates the likelihood of signal collisions at a transmission rate of 4 kbaud. Each line represents the length of time required to transmit each data frame <b>72</b> from each of the sensor assemblies <b>14</b>. <figref idref="DRAWINGS">FIG. 11</figref> illustrates how the increase in baud rate decreases the probability of overlapping data frames <b>72</b>. Each line represents a length of time to transmit one data frame <b>72</b> to the receiver assembly <b>16</b>. The shorter the total transmission time, the lower the probability of signal collision. Preferably, the system of this invention includes a baud rate of 10 kbaud as shown in <figref idref="DRAWINGS">FIG. 11</figref>, however, a worker skilled in the art would understand that different data transmission rates are within the contemplation of this invention.

Referring to <figref idref="DRAWINGS">FIGS. 1 and 12</figref> the receiver assembly <b>16</b> comprises an ASK receiver <b>52</b> and a FSK receiver <b>58</b>. The FSK receiver <b>58</b> receives signals from the sensor assemblies <b>14</b>. The ASK receiver receives signals from a key fob <b>22</b> for the remote keyless entry system <b>19</b> to initiate the unlocking of doors <b>20</b>. The receiver assembly <b>16</b> also includes an antenna <b>48</b> to receive transmissions from the key fob <b>22</b> and the sensor assemblies <b>14</b>. The receiver assembly <b>16</b> includes a low frequency driver <b>50</b> to emit a signal to the sensor assemblies <b>14</b> to initiate transmission by the sensor assemblies <b>14</b>.

The antenna <b>48</b> is preferably of a length one quarter that of the wavelength of the transmission received. Transmissions received by the antenna <b>48</b> proceed through a resistor <b>54</b> to the RF receiver <b>16</b>. A controller <b>60</b> controls which of the receivers <b>58</b> and <b>52</b> are engaged to receive incoming transmissions.

Transmission from the various sensor assemblies <b>14</b> include the unique identity code <b>68</b> (<figref idref="DRAWINGS">FIG. 8</figref>) relating to a specific sensor assembly <b>14</b>. The initialization or learning mode defines the specific sensor assemblies <b>14</b> disposed on a specific motor vehicle. Learning the specific identity codes <b>68</b> of each of the sensor assemblies <b>14</b> eliminates errant reception of other transmissions from other sensor assemblies <b>14</b> installed on other motor vehicles. Initialization occurs by matching the sensor assemblies <b>14</b> of a specific motor vehicle with the receiver assembly <b>16</b> of that motor vehicle. The receiver assembly <b>16</b> disposed within the motor vehicle <b>10</b> will receive numerous signals from surrounding RF transmitting sources such as radios, electrical appliances and other vehicle systems equipped with similar tire sensing systems.

Referring to <figref idref="DRAWINGS">FIG. 13</figref>, an embodiment of initialization includes placing the receiver assembly <b>16</b> (<figref idref="DRAWINGS">FIG. 1</figref>) in a learn mode and actuating each sensor assembly <b>14</b> through the use of a triggering device, schematically shown at <b>84</b>. The triggering device can be a magnet, a transponder located at a programming station or a low frequency emitter positioned on the motor vehicle. The triggering device <b>84</b> initiates each sensor assembly <b>14</b> in sequence to transmit the identity code <b>68</b>. The sequence of initiating transmission of the identity code <b>68</b> indicates the location of the sensor assembly <b>14</b> on the motor vehicle <b>10</b>. The first sensor assembly <b>14</b> triggered is the front left tire, the second is the front right and so on until all the tires on the motor vehicle have been triggered to transmit the identity code <b>68</b> to the receiver assembly <b>16</b>. The identity code <b>68</b> is stored sequentially to indicate the position of the specific sensor assembly <b>14</b>. The receiver assembly <b>16</b> learns which sensor assembly <b>14</b> belongs to the specific motor vehicle. In addition to the specific location on the sensor assembly on the motor vehicle such as the front right or front left tire is also recorded in the receiver assembly <b>16</b>. This operation is repeated any time the tires <b>12</b> of the motor vehicle are changed or rotated.

Another embodiment of initialization requires no external trigger. Instead an acceleration value from the motor vehicle <b>10</b> is communicated to the vehicle controller <b>18</b> and compared to accelerometer data transmitted from each of the sensor assemblies <b>14</b>. The accelerometer <b>34</b> of each sensor assembly <b>14</b> transmits acceleration information of the tire <b>12</b>. The acceleration value of each tire <b>12</b> is compared to the acceleration value provided by another vehicle system, such as the anti-lock braking system or transmission system (indicated schematically in <figref idref="DRAWINGS">FIG. 1</figref> at <b>86</b>). If the acceleration signals are equal within a predetermined tolerance value, the identity code <b>68</b> sent within the transmission from the sensor assembly <b>14</b> will be recorded as belonging to the specific motor vehicle.

The initialization or learning process using the compared values of acceleration may be repeated whenever the motor vehicle <b>10</b> is in a non-moving position for a predetermined length of time. The purpose of the relearning of the sensor assembly identification codes is to allow for changing or rotating of the tires <b>12</b> and thereby the sensor assembly <b>14</b>. The predetermined amount of time allows for the possibility that one of the sensor assemblies <b>14</b> may have been changed, for instance when a spare tire is installed.

In the instance, where a new tire, and thereby a new sensor assembly <b>14</b> is installed, the receiver assembly <b>16</b> receives the new identity code of the new sensor assembly <b>14</b> during initial movement of the motor vehicle <b>10</b>. The receiver assembly <b>16</b> compares the acceleration signal belonging to the new identity code of the new sensor <b>14</b> and compares it to the acceleration of the vehicle <b>10</b>. If the vehicle acceleration is comparable, the receiver assembly <b>16</b> will recognize the new sensor assembly <b>14</b> after a predetermined amount of time or number of data frames. This is transparent to the operator of the motor vehicle.

Referring to <figref idref="DRAWINGS">FIG. 14</figref>, in another embodiment of this invention, localization of each of the sensor assemblies <b>14</b> is established by comparing data obtained from another vehicle system <b>86</b> indicative of a turn of the motor vehicle <b>10</b>. The tires <b>12</b> of a motor vehicle travel different distances when turning. The inner tires <b>88</b> travel along a first radius indicated at r<b>1</b> and the outer tires <b>90</b> move along a second radius r<b>2</b>. Acceleration and turning data is compared to the acceleration at each wheel. Data transmitted from a sensor assembly <b>14</b> mounted to one of the inner tires <b>88</b> of the motor vehicle will indicate a lower acceleration than that of a sensor assembly <b>14</b> mounted to on of the outside wheels <b>90</b>. Therefore, the side that the sensor assembly <b>14</b> is positioned is indicated by the magnitude of acceleration of that tire relative to the acceleration and direction of the motor vehicle <b>10</b>. Accelerometer correlation determines whether the sensor assembly is on the left or right side of the motor vehicle <b>10</b>, however, this does not indicate whether the sensor assembly <b>14</b> is a front or rear tire.

In one embodiment of localization the front to rear location of the tire <b>12</b> is accomplished by detecting signal strength of the transmission sent from each of the sensor assemblies <b>14</b>. In this embodiment, the receiver assembly <b>16</b> includes front and rear antennas <b>92</b>, <b>94</b>. Transmissions received at each antenna <b>92</b>,<b>94</b> are measured for field strength. The rear antenna <b>94</b> will receive transmissions having higher field strength from the sensor assemblies <b>14</b> disposed on the rear tires of the motor vehicle <b>10</b>. The front antenna <b>92</b> will receive a stronger transmission from sensor assemblies <b>14</b> disposed on the front tires of the motor vehicle <b>10</b>. The field strength data provides the data indicating the front or rear position of each sensor assembly <b>14</b> and the acceleration data correlated to the turning radius of the motor vehicle <b>10</b> provides the left or right position of each of the sensor assemblies <b>14</b>.

Referring to <figref idref="DRAWINGS">FIG. 15</figref>, another embodiment of localization combines low frequency transmissions with correlation of acceleration to determine the position of the sensor assemblies <b>14</b>. Low frequency emitters <b>96</b> are positioned to initiate transmission from the rear sensor assemblies <b>14</b>. A transmission from the low frequency emitter triggers the transmission of the rear sensor assemblies <b>14</b> that is then received by the receiver assembly <b>16</b> to indicate a rear location of the tires <b>12</b>. This provides the data required to determine the front and rear position of any particular sensor assembly <b>14</b>. The left and right position is determined by correlating accelerometer data obtained from each of the sensor assemblies <b>14</b>. Further, a worker knowledgeable in the art will recognize that other combination of low frequency initiating transmissions and correlation of accelerometer data can be used to determine the specific location of any of the sensor assemblies <b>14</b> disposed on the motor vehicle <b>10</b>.

The receiver assembly <b>16</b> of this system is also used with the remote keyless entry system <b>19</b>. The receiver assembly <b>16</b> is configured to receive transmission from both the sensor assemblies <b>14</b> and the key fob <b>22</b> (FIG. <b>1</b>). Although a key fob <b>22</b> is specifically described it is within the contemplation of this invention that the remote entry system <b>19</b> include other active or passive transmitting means to initiate entry or operation of the motor vehicle <b>10</b>.

The receiver assembly <b>16</b> includes the ASK receiver <b>52</b> and the FSK receiver <b>58</b>. This configuration allows the receiver assembly <b>16</b> to be used for both the remote keyless entry system <b>19</b> and the tire monitoring system.

ASK transmissions are favorable for situations where the transmitter and receiver are substantially stationary. The ASK radio frequency transmission is easily disrupted by abrupt changes in received field strength and therefore are not favorable sending transmission from a moving object such as the tires <b>12</b> of a motor vehicle <b>10</b>. The changes from received field strength can change for any number or reasons within a motor vehicle including interference created by other onboard systems, to the specific environment present at the time of the signal. However, the ASK provides for greater signal power which is desirable for the remote keyless entry system of this invention. The ASK transmission allows for higher peak output field strength, relative to a comparable FSK transmission. However, the ASK transmission decreases typical battery life and is therefore not desirable for applications such as tire condition sensing that require longer battery life due to the difficulty of changing batteries of the sensor assemblies disposed within the tire of the motor vehicle.

FSK transmissions are favorable for conditions were the transmitter or receiver are moving during data transmission. As appreciated, rotation of a tire will introduce amplitude variations in the transmission caused by the changes in interference patterns. If sensor assembly <b>14</b> data was transmitted by way of an ASK transmission, the noise caused by rotation of the tire would cause data in the transmission to become corrupted. However, an FSK transmission is amplified upon receipt to effectively remove any amplitude disturbances. Further, the FSK transmission is less power intensive and therefore more adaptable to the sensor assembly application that requires longer battery life.

Referring to <figref idref="DRAWINGS">FIG. 12</figref>, the receiver assembly <b>16</b> defaults to sending any transmission to the ASK receiver <b>52</b>. The ASK receiver <b>52</b> operates at a lower power and is therefore the default receiver that is on when the receiver assembly <b>16</b> is activated. The ASK receiver <b>52</b> is engaged while the motor vehicle <b>10</b> is stopped or parked. Preferably, the ASK receiver <b>52</b> is engaged in response to the speed of the motor vehicle being below a predetermined speed. Preferably, the predetermined speed is 10 mph. Above 10 mph, the receiver assembly <b>16</b> will change over to the FSK receiver <b>58</b>. The switch is initiated because it is unlikely that the remote keyless entry system <b>19</b> will be activated while the vehicle <b>10</b> is traveling at speed. The FSK receiver <b>58</b> will then receive transmissions from the sensor assemblies <b>14</b>.

The conditions of the motor vehicle <b>10</b> traveling above the desired speed or in a parked position provide definite indicators for the switch between FSK and ASK receivers <b>58</b>, <b>52</b>. However, when the vehicle <b>10</b> is idling, for instance in a traffic jam, but not moving at the desired speed to switch from the ASK receiver <b>52</b> and the FSK receiver <b>58</b> the system will not switch over to the FSK receiver <b>58</b> unless another conditions is satisfied. Each transmission <b>64</b> (<figref idref="DRAWINGS">FIG. 8</figref>) includes the ASK wake up signal <b>66</b> that is sent prior to the FSK transmission. The ASK wake up signal <b>66</b> alerts the receiver assembly <b>16</b> to incoming FSK transmission, which causes the receiver assembly <b>16</b> to switch over to the FSK receiver <b>58</b>. The switch over allows the receiver assembly <b>16</b> to accept data indicative of tire conditions from the sensor assemblies <b>14</b> while the automobile is parked or idling in traffic.

Preferably, each of the sensor assemblies <b>14</b> will transmit a signal indicative of tire conditions at differing rates depending on the speed of the motor vehicle. At speeds above a predetermined speed the sensor assemblies <b>14</b> will transmit tire condition data at a greater frequency. At lower speeds, indicative of a parked vehicle, the sensor assemblies <b>14</b> transmit at a lower rate. Preferably, the predetermined speed is 10 mph and the sensor assemblies <b>14</b> will transmit signals indicative of tire conditions once every minute. Below the 10 mph predetermined speed threshold the sensor assemblies <b>14</b> will transmit signals only after sensing a change in tire pressure above a desired amount indicative of a tire <b>12</b> losing air pressure. Once an initial loss of pressure is sensed, the sensor assemblies <b>14</b> are triggered to transmit signals at one-minute intervals. Although, specific speeds and intervals of data transmission are discussed, a worker knowledgeable in the art will understand that it is within the contemplation of this invention to use other speeds and data transmission intervals according to specific application criteria. The selective actuation of the transmitter <b>40</b> for each sensor assembly and the switching between the ASK and FSK receivers <b>52</b>,<b>58</b> prevent signal collisions between ASK and FSK transmission emitted by the remote keyless entry system <b>19</b> and the tire monitoring system. Preventing signal collisions optimizes function of the receiver assembly <b>16</b>.

The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.